Oxygen radical absorbance capacity

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Oxygen Radical Absorbance Capacity (ORAC) is a method of measuring antioxidant capacities of different foods.[1][2] It was developed by the scientists at the National Institute on Aging in the National Institutes of Health (NIH) in Bethesda, Maryland, but this method is not approved by the NIH. Recently, US Department of Agriculture USDA listed a database of the ORAC value in its home page (www.usda.gov) without evaluation. A wide variety of foods have been tested using this methodology, with certain spices, berries and legumes rated very highly[3]. Correlation between the high antioxidant capacity of fruits and vegetables, and the positive impact of diets high in fruits and vegetables, is believed to play an important role in the free-radical theory of aging.

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[edit] Method

The original idea of the ORAC assay is based on Glazer's study. The assay measures the oxidative degradation of the fluorescent molecule (either beta-phycoerythrin or fluorescein) after being mixed with free radical generators such as azo-initiator compounds. Azo-initiators are considered to produce peroxyl free radical by heating, which damages the fluorescent molecule,resulting in the loss of fluorescence. Antioxidant is able to protect the fluorescent molecule from the oxidative degeneration. The degree of protection will be quantified using a fluorometer. Fluorescein is currently used most as a fluorescent probe. Equipment that can automatically measure and calculate the capacity is commercially available (Biotek, Roche Diagnostics).

The fluorescent intensity decreases as the oxidative degeneration proceeds, and this intensity is typically recorded for 35 minutes after the addition of the azo-initiator (free radical generator). The degeneration (or decomposition) of fluorescein that is measured as the fluorescence delay becomes less prominent by the presence of antioxidants. Decay curves (fluorescence intensity vs. time) are recorded and the area between two decay curves (with or without antioxidant) is calculated. Subsequently, the degree of antioxidant-mediated protection is quantified using the antioxidant trolox (a vitamin E analogue) as a standard. Different concentrations of trolox are used to make a standard curve, and test samples are compared to this. Results for test samples (foods) have been published as "trolox equivalents" or TE.[4]

One benefit of using the ORAC method to evaluate substance's antioxidant capacity is that it takes into account samples with and without lag phases of their antioxidant capacities. This is especially beneficial when measuring foods and supplements that contain complex ingredients with various slow and fast acting antioxidants, as well as ingredients with combined effects that cannot be pre-calculated.

Drawbacks of this method are: 1) only antioxidant activity against particular (probably mainly peroxyl) radicals is measured; 2) the nature of the damaging reaction is not characterized; and 3) there is no evidence that free radical is involved in this reaction. Moreover, the relationship between ORAC values and the health benefit has not been established.

[edit] Food Sources

In 2007, scientists with the United States Department of Agriculture published an updated list of ORAC values for 277 foods commonly consumed by the U.S. population (fruits, vegetables, nuts, seeds, spices, grains, etc.).[5] Values were reported as micromoles of Trolox equivalents (TE, vitamin E derivative) per 100 grams both for lipid-soluble ("lipophilic" as for carotenoids) and water-soluble ("hydrophilic" as for phenolics) antioxidant chemicals in foods, thus were a sum of lipophilic and hydrophilic values or total ORAC. These values are considered to be more accurate than previously published ORAC numbers because lipophilic values were being included for the first time.

USDA data on foods with high levels of antioxidant phytochemicals
Food Serving size Antioxidant capacity per serving size[6]
Cinnamon, ground 100 grams 267,536
Aronia black chokeberry (Aronia melanocarpa) 100 grams 16062
Small Red Bean ½ cup dried beans 13727
Wild blueberry 1 cup 13427
Red kidney bean * ½ cup dried beans 13259
Pinto bean ½ cup 11864
Blueberry 1 cup (cultivated berries) 9019
Cranberry 1 cup (whole berries) 8983
Artichoke hearts 1 cup, cooked 7904
Blackberry 1 cup (cultivated berries) 7701
Prune ½ cup 7291
Raspberry 1 cup 6058
Strawberry 1 cup 5938
Red Delicious apple 1 apple 5900
Granny Smith apple 1 apple 5381
Pecan 1 oz 5095
Sweet cherry 1 cup 4873
Black plum 1 plum 4844
Russet potato 1, cooked 4649
Black bean ½ cup dried beans 4181
Plum 1 plum 4118
Gala apple 1 apple 3903

* Raw and undercooked red kidney beans contain a natural protein toxin that can cause mild to severe food poisoning.[7] Cooking by soaking, then boiling the beans breaks down the toxin to a safe level.[8] However, as with nearly all vegetables, conventional boiling reduces the ORAC value significantly, while steaming retains more of the antioxidants.[9]

The values for other spices and high-ORAC fruits such as black elderberry (Sambucus nigra) have not been included in the chart which, according to the new data published in 2007, have among the highest values yet recorded for common North American foods.[10]

[edit] Comparisons of ORAC values

When comparing ORAC data, care must be taken to ensure that the units and food being compared are similar. Some evaluations will compare ORAC units per grams dry weight, others will evaluate ORAC units wet weight and still others will look at ORAC units/serving. Under each evaluation, different foods can appear to have higher ORAC values. Although a raisin has no more antioxidant potential than the grape from which it was dried, raisins will appear to have a much higher ORAC value per gram wet weight than grapes due to their reduced water content. Likewise, watermelons large water content can make it appear as though they are very low in antioxidants. Additionally, considering the ORAC value per calorie could be of some utility, as understanding just how much antioxidizing potential one could incorporate from a product into one's diet would determine the real utility of the product.

The range of ORAC for common fruits was around 1.40 micromoles TE per gram (watermelon) to 95 (cranberry). Lowbush blueberry (wild blueberry) was also very high at 92.6 µmol/g. For vegetables or legumes, it was 1.15 (cucumber) to 149 small red (red kidney bean); for nuts, 7.19 (cashew) to 179.4 (pecan); and for dried fruits, 23.87 (medjool dates) to 85.78 (prune). By comparison, different species of apples had ORAC values of 22.10 to 42.75 micromoles TE per gram, white potato was under 11, peanut was 31.66 and tomato about 4.00 Spices (clove, cinnamon) showed the highest ORAC values (>2500, converted to micromoles TE per gram). Cocoa has a high ORAC value, giving baking chocolate a value of 1032 and milk chocolate an average of 71.30.

Recently, a number of health food companies have capitalized on the ORAC rating, with dozens selling concentrated supplements that they claim to be "the number one ORAC product". Most of these values have never been published in the scientific literature so are difficult to evaluate. It is not known whether such values are accurate or how absorbable and functional these concentrated antioxidants are in the human body.

[edit] References

  1. ^ Cao G, Alessio H, Cutler R (1993). "Oxygen-radical absorbance capacity assay for antioxidants". Free Radic Biol Med 14 (3): 303–11. doi:10.1016/0891-5849(93)90027-R. PMID 8458588. 
  2. ^ Ou B, Hampsch-Woodill M, Prior R (2001). "Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe". J Agric Food Chem 49 (10): 4619–26. doi:10.1021/jf010586o. PMID 11599998. 
  3. ^ [1] Oxygen Radical Absorbance Capacity of Selected Foods - 2007; Nutrient Data Laboratory, Agricultural Research Service, United States Department of Agriculture, November 2007
  4. ^ Huang D, Ou B, Prior R (2005). "The chemistry behind antioxidant capacity assays". J. Agric. Food Chem. 53 (6): 1841–56. doi:10.1021/jf030723c. PMID 15769103. 
  5. ^ Nutrient Data Laboratory, Agriculture Research Service, US Department of Agriculture, Oxygen radical absorbance capacity (ORAC) of Selected Foods - 2007.[2]
  6. ^ Units are Total Antioxidant Capacity per serving in units of micromoles of Trolox equivalents.
  7. ^ "Red Kidney Bean Food Poisoning". http://apex.oracle.com/pls/otn/f?p=2400:1001:674479108843189::::F2400_P1001_BACK_PAGE,F2400_P1001_ARCHIVE_NUMBER,F2400_P1001_USE_ARCHIVE:1001,20071229.4170,Y. Retrieved on October 23 2008. International Society for Infectious Diseases ProMED-mail email bulletin, Dec 29, 2007.
  8. ^ "Food for thought: Are uncooked red kidney beans poisonous?". http://findarticles.com/p/articles/mi_qn4158/is_19990207/ai_n14215824. Retrieved on October 23 2008. The Independent, UK newspaper, February 7, 1999.
  9. ^ "Antioxident Properties of Vegetables, Herbs, Spices, Salad Dressings". http://content.herbalgram.org/naturemade/HerbClip/pdfs/070355-297.pdf. Retrieved on October 23 2008. HerbClip newsletter, January 31, 2006; Review of a Feb. 2005 British Journal of Nutrition study that found "Steamed vegetables retained about 80% of the phenolic and ORAC values of raw vegetables; boiled vegetables retained only 30% of antioxidants."
  10. ^ Oxygen Radical Absorbance Capacity of Selected Foods - 2007; Nutrient Data Laboratory, Agricultural Research Service, United States Department of Agriculture, November 2007.[3]

[edit] See also

[edit] External links

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